Abstract:

A hydraulically servocontrolled transmission for a road vehicle provided
with an internal combustion engine; the servocontrolled transmission
displays: a servocontrolled mechanical gearbox operated by at least one
first hydraulic actuator; a servocontrolled clutch operated by at least
one second hydraulic actuator; a hydraulic circuit comprising a hydraulic
accumulator, which contains pressurised control fluid which is used by
the hydraulic actuators, and a pump, which is directly operated by the
internal combustion engine to supply pressurised control fluid to the
hydraulic accumulator; a park-lock device operatable to block the
rotation of the driving wheels; and a control unit, which, when the
internal combustion engine is turned off, uses the remaining pressure of
the control fluid within the hydraulic accumulator to bring the
servocontrolled mechanical gearbox in a neutral position.

Claims:

1) A servocontrolled hydraulically transmission (7) for a road vehicle (1)
provided with an internal combustion engine (5); the servocontrolled
transmission (7) comprises:a servocontrolled mechanical gearbox (12)
operated by at least one first hydraulic actuator (16, 17) and provided
with a primary shaft (13) connectable to the drive shaft (6) and with a
secondary shaft (14) connected to a transmission shaft (8) which
transmits the motion to the driving wheels (3);a servocontrolled clutch
(15) operated by at least one second hydraulic actuator (18) and
interposed between the driving shaft (6) and the primary shaft (13) of
the gearbox (12) to connect and disconnect the drive shaft (6) to the
primary shaft (13) of the gearbox (12); anda hydraulic circuit (19)
comprising a hydraulic accumulator (21), which contains pressurised
control fluid which is used by the hydraulic actuators (16, 17, 18), and
a pump (22), which is directly operated by the internal combustion engine
(5) to supply the pressurised control fluid to the hydraulic accumulator
(21);the servocontrolled transmission (7) is characterised in that it
comprises:a park-lock device (24) operatable to block the rotation of the
driving wheels (3); anda control unit (11), which, when the internal
combustion engine (5) is turned off, uses the remaining pressure of the
control fluid within the hydraulic accumulator (21) to bring the
servocontrolled mechanical gearbox (12) in a neutral position.

2) A servocontrolled transmission (7) according to claim 1, wherein the
pump (22) is operated by obtaining the motion from a drive shaft (6) of
the internal combustion engine (5).

3) A servocontrolled transmission (7) according to claim 2, wherein the
pump (22) is operated by obtaining the motion directly from the drive
shaft (6) of the internal combustion engine (5).

4) A servocontrolled transmission (7) according to claim 2, wherein the
pump (22) is operated by obtaining the motion from a flywheel set in
rotation by the drive shaft (6) of the internal combustion engine (5).

5) A servocontrolled transmission (7) according to claim 4, wherein the
pump (22) is operated by an auxiliary spindle which is coaxial to the
primary shaft (13) of the servocontrolled gearbox (12) and moved by the
flywheel.

6) A servocontrolled transmission (7) according to claim 2, wherein the
pump (22) is operated obtaining the motion from the primary shaft (13) of
the servocontrolled mechanical gearbox (12).

7) A servocontrolled transmission (7) according to claim 6, wherein the
control unit (11) automatically brings the servocontrolled mechanical
gearbox (12) in a neutral position if the clutch (15) remains in the open
position for a time longer than the determined time interval.

8) A servocontrolled transmission (7) according to claim 7, wherein the
control unit (11) closes the servocontrolled clutch (15) to operate the
pump (22) again if the pressure within the hydraulic accumulator (21)
falls to values which are too low.

9) A servocontrolled transmission (7) according to claim 1, wherein the
park-lock device (24) is operatable by the driver by means of a manually
operatable control.

10) A servocontrolled transmission (7) according to claim 9, wherein the
park-lock device (24) is electrically interfaced with a safety device in
a start-up block so that the extraction of a start-up key is possible
only when the park-lock device (24) is active to block the rotation of
the driving wheels (3).

11) A method for the control of a hydraulically servocontrolled
transmission (7) for a road vehicle (1) provided with an internal
combustion engine (5); the servocontrolled transmission (7) comprises:a
servocontrolled mechanical gearbox (12) operated by at least one first
hydraulic actuator (16, 17) and provided with a primary shaft (13)
connectable to the drive shaft (6) and with a secondary shaft (14)
connected to a transmission shaft (8) which transmits the motion to the
driving wheels (3);a servocontrolled clutch (15) operated by at least one
second hydraulic actuator (18) and interposed between the drive shaft (6)
and the primary shaft (13) of the gearbox (12) to connect and disconnect
the drive shaft (6) to/from the primary shaft (13) of the gearbox (12);a
hydraulical circuit (19) comprising a hydraulic accumulator (21), which
contains pressurised control fluid which is used by the hydraulic
actuators (16, 17, 18), and a pump (22), which is directly operated by
the internal combustion engine (5) to supply pressurised control fluid to
the hydraulic accumulator (21); anda park-lock device (24) to block the
rotation of the driving wheels (3);the method for the control of the
servocontrolled transmission (1) comprises the step of bringing the
servocontrolled mechanical gearbox (12) in a neutral position when the
internal combustion engine (5) is turned off by using the remaining
pressure of the control fluid within the hydraulic accumulator (21).

12) A method according to claim 11, comprising the further step of
allowing the extraction of a start-up key from a start-up block only when
the park-lock device (24) is active to block the rotation of the driving
wheels (3).

Description:

PRIORITY

[0001]The present application claims priority to the European application
entitled A HYDRAULICALLY SERVOCONTROLLED TRANSMISSION FOR A ROAD VEHICLE
PROVIDED WITH AN INTERNAL COMBUSTION ENGINE, having application number
07425011.9, filed on Friday, Jan. 12, 2007, which is incorporated herein
by reference.

TECHNICAL FIELD

[0002]The present invention relates to a hydraulically servocontrolled
transmission for a road vehicle provided with an internal combustion
engine.

BACKGROUND ART

[0003]Servocontrolled transmissions, which are structurally similar to a
manual servocontrolled transmission of the traditional type except for
the fact that the pedal of the clutch and the gear selection lever
operated by the driver are replaced by corresponding electrical or
hydraulic servo controls, are increasingly widespread. By using a
servocontrolled transmission the driver must only send the control unit
of the transmission the command to up-shift or down-shift and the control
unit of the transmission autonomously carries out the change of gear by
acting both on the engine and on the servo controls associated to the
clutch and gearbox.

[0004]Generally, the servo control of the gearbox and the servo control of
the clutch are of the hydraulic type and comprise corresponding hydraulic
actuators connected to a common hydraulic circuit which comprises a
storage tank containing the control fluid used by the hydraulic actuators
(typically oil) at an ambient pressure, a hydraulic accumulator
containing pressurised control fluid, an electrical pump which picks up
the control fluid from the storage tank and supplies the pressurised
control fluid to the hydraulic accumulator, and a number of
electrovalves, which are adapted to selectively connect chambers of the
hydraulic actuators to the storage tank and to the hydraulic accumulator.
In other terms, in the known applications which are commercialised at
present, the pump of the hydraulic circuit is actuated by an electrical
motor (electrical pump assembly), which is fed by the motor vehicle
battery and may therefore work independently of the state of motion of
the thermal engine.

[0005]The use of an electrical pump assembly for the hydraulic circuit has
several drawbacks: the electrical motor may be liable to ruptures
(reduced reliability in time) especially in heavy use conditions, the
electrical pump assembly is noisy, and finally the electrical pump
assembly has installation criticalities as it requires an appropriate
cooling of the electrical motor.

[0006]To solve the above described drawbacks, it has been suggested to
eliminate the electrical motor and operate the hydraulic circuit pump by
obtaining the motion directly from the thermal motor.

[0007]For instance, patent application GB2339606A describes the
possibility of operating a pump of a hydraulic circuit of a transmission
system obtaining the motion directly from the thermal engine;
specifically GB2339606 provides the use of an auxiliary electrical motor
when the motion obtained from the thermal engine is insufficient.

[0008]Also U.S. Pat. No. 5,474,428A1 describes the possibility of
operating a pump of a hydraulic circuit of a transmission system
obtaining the motion directly from the thermal engine or, as an
alternative, by using an electrical motor; specifically, the oil supplied
by the pump may be used both for lubricating the transmission and for
operating the transmission during a change of gear.

[0009]However, the above described solutions which are known for
eliminating the electrical motor and operating the pump of the hydraulic
circuit thus obtaining the motion directly from the thermal engine are
not completely satisfactory, because they provide in any case the use of
a small auxiliary electrical motor which is operated when the motion
obtained from the thermal engine is insufficient; accordingly, such known
solutions are complicated, expensive and voluminous.

DISCLOSURE OF THE INVENTION

[0010]It is the object of the present invention to provide a hydraulically
servocontrolled transmission for a road vehicle provided with an internal
combustion engine, such a servocontrolled transmission being free from
the above described drawbacks and, especially, being easy and
cost-effective to implement.

[0011]According to the present invention there is provided a hydraulically
servocontrolled transmission for a road vehicle provided with an internal
combustion engine as claimed in the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]The present invention will now be described with reference to the
accompanying drawings, which show a non-limitative example of embodiment
thereof, in which:

[0013]FIG. 1 is a diagrammatic plan view of a rear wheel drive motor
vehicle provided with a servocontrolled transmission made according to
the present invention;

[0014]FIG. 2 is a diagrammatic view of a thermal engine and of the
servocontrolled transmission of the motor vehicle in FIG. 1; and

[0015]FIG. 3 is a diagram of a part of a hydraulic circuit of the
servocontrolled transmission in FIG. 2.

PREFERRED EMBODIMENTS OF THE INVENTION

[0016]In FIG. 1, numeral 1 indicates, as a whole, a motor vehicle provided
with two front wheels 2 and two rear driving wheels 3 which receive the
driving torque from a power system 4.

[0017]The power system 4 comprises an internal combustion engine 5, which
is arranged in a front position and is provided with a drive shaft 6
which rotates at an angular speed ωm, and a servocontrolled
transmission 7, which is arranged in a front position, is housed in a
bell integral with the internal combustion engine 5 and transmits the
driving torque generated by the internal combustion engine 5 to the rear
driving wheels 3. From the servocontrolled transmission 7, a transmission
shaft 8 extends, which ends in a differential 9, from which a pair of
axle shafts 10 extends, with each of the axle shafts being integral with
a rear driving wheel 3. The motor vehicle 1 comprises an electrical
control unit 11 (diagrammatically shown), which controls the power system
4 and therefore drives both the internal combustion engine 5 and the
servocontrolled transmission 7.

[0018]According to what is shown in FIG. 2, the servocontrolled
transmission 7 comprises a servocontrolled mechanical gearbox 12 provided
with a primary shaft 13 which rotates at an angular speed ω1
and is connectable to the drive shaft 6 and with a secondary shaft 14
which rotates at an angular speed ω2 and is connected to the
transmission shaft 8 that transmits the motion to the driving wheels 3. A
servocontrolled disc clutch 15 is interposed between the drive shaft 6
and the primary shaft 13 of the gearbox 12 to connect and disconnect the
drive shaft 6 to/from the primary shaft 13 of the gearbox 12.

[0019]The servocontrolled mechanical gearbox 12 is operated by a hydraulic
actuator 16 to engage/disengage a gear and by a hydraulic actuator 17 to
select a gear; the servocontrolled clutch 15 is operated by a single
hydraulic actuator 18 to shift the clutch 15 itself between an open
position and a closed position. The hydraulic actuators 16, 17 and 18 are
driven by the electric control unit 11 and are connected to a hydraulic
circuit 19 (shown in FIG. 3).

[0020]According to what is shown in FIG. 3, the hydraulic circuit 19
comprises a storage tank 20 containing the control fluid used by the
hydraulic actuators 15, 16 and 17 (typically oil) at an ambient pressure,
a hydraulic accumulator 21 containing pressurised control fluid, a pump
22 which picks up the control fluid from the storage tank 20 and supplies
the pressurised control fluid to the hydraulic accumulator 21, and three
electrovalves 23, which are adapted to selectively connect chambers of
the corresponding hydraulic actuators 15, 16 and 17 with the storage tank
20 and with the hydraulic accumulator 21. Specifically, a corresponding
three-way electrovalve 23 is associated to each chamber of the hydraulic
actuators 15, 16 and 17, with the three-way electrovalve 23 being adapted
to maintain the chamber isolated to maintain the control fluid within the
chamber constant, to connect the chamber to the storage tank 20 to
discharge the control fluid present within the chamber or to connect the
chamber to the hydraulic accumulator to supply the control fluid within
the chamber.

[0021]According to what is shown in FIG. 2, the servocontrolled
transmission 7 comprises a park-lock device 24 operatable by the driver
by means of a control operated manually to block the rotation of the
driving wheels 3. According to a preferred embodiment, the park-lock
device 24 is electrically interfaced with the safety device in a start-up
block of the motor vehicle 1 so that the extraction of the start-up key
for the internal combustion engine 5 is possible only when the park-lock
device 24 is active to block the rotation of the driving wheels 3. The
park-lock device 24 may be arranged within the servocontrolled mechanical
gearbox 12 to act on the secondary shaft 14 (as shown in FIG. 2), or the
park-lock device 24 may be arranged within the differential 9 to act on
the transmission shaft 8 or on the axle shafts 10.

[0022]Furthermore, the pump 22 is directly actuated by the internal
combustion engine 5 to supply pressurised control fluid to the hydraulic
accumulator 21. When the internal combustion engine 5 is turned off, the
control unit 11 uses the remaining pressure of the control fluid within
the hydraulic accumulator 21 to bring the servocontrolled mechanical
gearbox 12 in a neutral position. In this manner, it is always possible
to start up the internal combustion engine 5 again without needing to act
on the servocontrolled clutch 15; furthermore, in virtue of the action of
the park-lock device 24 (which needs to be operated in order to extract
the start-up key) the motor vehicle 1 remains in any case braked in the
parked position even if the servocontrolled mechanical gearbox 12 is in
neutral position.

[0023]According to an embodiment shown in FIG. 2, the pump 22 is operated
obtaining the motion from the driving shaft 6 of the internal combustion
engine 5 by means of a belt transmission; in this case, the pump 22
receives the motion when the internal combustion engine 5 is running
independently of the state of the servocontrolled clutch 15.

[0024]According to an alternative embodiment (not shown), the pump 22 is
operated obtaining the motion from the driving shaft 6 of the internal
combustion engine 5 by means of an auxiliary shaft, which is coaxial to
the primary shaft 13 of the servocontrolled gearbox 12 and is moved by
the flywheel; in this case as well, the pump 22 receives the motion when
the internal combustion engine 5 is running independently of the state of
the servocontrolled clutch 15.

[0025]According to a further embodiment (not shown), the pump 22 is
operated by obtaining the motion of the primary shaft 13 of the
servocontrolled mechanical gearbox 12; in this case, the pump 22 receives
the motion when the internal combustion engine 5 is running and the
servocontrolled clutch 15 is in a closed position. According to such an
embodiment, the control unit 11 automatically brings the servocontrolled
mechanical gearbox 12 in a neutral position if the servocontrolled clutch
15 remains in the open position for a time longer than the determined
time interval of 10 seconds, by way of example. By operating in this
manner, the control unit 11 may decide to close the servocontrolled
clutch 15 to operate the pump 22 again if the pressure within the
hydraulic accumulator 21 falls to values which are too low.

[0026]According to a further embodiment (not shown), it is possible to use
a single operating hydraulic system for the oil used by the hydraulic
actuators 16, 17 and 18 and for the oil used for the lubrication of the
servocontrolled mechanical gearbox 12.

[0027]The above described servocontrolled transmission 7 is especially
reliable and simple and cost-effective to implement in virtue of the
absence of any type of electrical motor connected to the pump 22 of the
hydraulic circuit 19.

[0028]A traditional servocontrolled transmission 7 leaves the motor
vehicle 1 turned off and parked with a gear engaged; instead, after the
internal combustion engine has been turned off, the above described new
servocontrolled transmission always and automatically brings the
servocontrolled mechanical gearbox 12 in neutral and the function of
maintaining the motor vehicle 1 still is carried out by the park-lock
device 24.

[0029]A traditional servocontrolled transmission 7 allows the start up of
the internal combustion engine only after having opened the clutch and
brought the gear in neutral; accordingly, in a traditional
servocontrolled transmission 7 the actual start up of the internal
combustion engine is always delayed with respect to the control of the
driver. Instead, the above described new servocontrolled transmission 7
allows the start up of the internal combustion engine 5 immediately and
without any delay as the servocontrolled mechanical gearbox 12 is already
in a neutral position.